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Hydrogen storage: Engineering and performance

Where the energy goes when hydrogen goes into storage

What this tab covers Engineering and operating performance: round-trip efficiency, whether power and energy can be scaled separately, footprint and siting, and safety.

The losses in hydrogen storage come mostly from getting hydrogen into a dense state and back out. Underground storage is cheap per unit of energy but fixed to geology; tanks and carriers are flexible but costly or lossy.

Round-trip efficiency

Unfavourable

For the storage step alone, compression is the lightest penalty: the theoretical minimum for 700 bar is about 4% of hydrogen's energy content (lower heating value, 33.3 kWh per kg), and measured on-site compression to 350 bar has used about 5-20%. Liquefaction today takes 10-13 kWh per kg, or 30-40%, with large future plants projected at about 8 kWh per kg. LOHC release needs about 11 kWh of heat per kg, about a third of the hydrogen's energy (calculated), although binding the hydrogen gives off about 9 kWh of heat that can be reused. Converting electricity to hydrogen and back adds much larger electrolyser and turbine or fuel cell losses, so electricity-to-electricity efficiency is well below that of batteries.13

Compression to 700 bar 1.35 kWh/kg theoretical; actual 350 bar on-site 1.7-6.4 kWh/kg1 Liquefaction, typical actual 10-13 kWh/kg (30-40% of LHV)1 LOHC release heat about 11 kWh(thermal)/kg H23

Power and energy decoupling

Favourable

Hydrogen storage is fully decoupled: electrolyser size sets charging power, the turbine or fuel cell sets discharging power, and the cavern or tank volume sets energy. The marginal cost of extra energy falls steeply with scale underground. Using a published US national-laboratory cost correlation (Papadias and Ahluwalia, 2021), salt cavern capital cost falls from about USD 95 per kg stored at 100 t to about USD 25 per kg at 1,000 t, while buried pipe storage stays near USD 510-530 per kg (calculated; dollar year not stated). At ACES Delta in Utah, now majority owned by Chevron with Mitsubishi Power, all 220 MW of electrolysers were reported running at full load in early 2026, feeding two salt caverns.891314

Salt cavern capex, 100 t vs 1,000 t usable about USD 95/kg vs USD 25/kg (calculated)9 Pipe storage capex, 100-1,000 t about USD 510-530/kg (calculated)9 ACES Delta, Utah 220 MW electrolysis, two caverns of about 4.5 million barrels each8

Footprint and siting flexibility

Mixed

Salt caverns use little surface land but exist only where salt beds are found; depleted fields need proven tight geology. Tanks and LOHC can go almost anywhere, and LOHC can use ordinary fuel logistics. Metal hydrides suit small home or site storage below 100 C and medium stores, but researchers judge them less promising for large volumes.3610

Safety and thermal runaway risk

Mixed

There is no thermal runaway as in lithium batteries, but hydrogen is flammable from about 4% by volume in air, burns with an almost invisible flame and can embrittle metals. Liquid storage adds cryogenic hazards and boil-off. In the US, NFPA 2 (Hydrogen Technologies Code), first issued in 2006 and now in its 2026 edition, covers the production, storage, transfer and use of hydrogen and sets setback distances; for gaseous hydrogen these are based on an 8% concentration criterion, the level at which ignition can be sustained, rather than the 4% lower flammability limit. In the EU, the Seveso III major-hazard directive applies to sites holding 5 t of hydrogen (lower tier) or 50 t (upper tier). LOHC avoids most of the pressure and cryogenic risk.3111215

Hydrogen lower flammability limit 4% by volume in air11 NFPA 2 setback basis (gaseous H2) 8% concentration criterion11 Seveso III hydrogen thresholds 5 t lower tier; 50 t upper tier12

Sources

  1. DOE Hydrogen Program Record 9013: Energy requirements for hydrogen gas compression and liquefaction US Department of Energy, 2009
  2. LOHC brochure Hydrogenious LOHC Technologies, 2025
  3. Underground hydrogen storage: application of resource management (UNECE Resource Management Week) IEA Hydrogen Technology Collaboration Programme, 2021
  4. Advanced Clean Energy Storage (ACES Delta) project summary US DOE Loan Programs Office, 2022
  5. Bulk hydrogen storage cost model (implements Papadias and Ahluwalia 2021, Int. J. Hydrogen Energy) H2Integrate documentation (NREL, renamed National Laboratory of the Rockies in 2025), 2025
  6. Metal hydrides for hydrogen storage: identification and evaluation of stationary and transportation applications (Drawer, Lange, Kaltschmitt), Journal of Energy Storage 77, 109988 Elsevier (repository copy, Tecnalia), 2024
  7. H2IQ Hour: Update on changes to the NFPA Hydrogen Technologies Code (NFPA 2); setback distances for bulk liquefied hydrogen storage US DOE Hydrogen and Fuel Cell Technologies Office / Sandia, 2023
  8. Directive 2012/18/EU (Seveso III), Annex I legislation.gov.uk (EU directive text as adopted), 2012
  9. Chevron assumes lead role in largest US hydrogen storage project Journal of Petroleum Technology (SPE), 2023
  10. Hydrogen production soars as ACES Delta's electrolyzers hit full load Hydrogen Fuel News, 2026
  11. NFPA 2-2026: Hydrogen Technologies Code (catalogue listing) ANSI Webstore / NFPA, 2026